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The Modern Apprentice



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Raptor biology is a fascinating subject. Understanding the basics of the bird's body and its functions will make you a better falconer.

Alula Three small, stiff feathers control the flow of air over the wing during flight.

Beak The keratin covering of the mouth protecting the tongue and mouth opening.

Blood feathers Feathers which still are still growing and have blood supplied through the shaft.

Cere The smooth, featherless skin just above the beak where it attaches to the forehead. Also called the operculum.

Choanal slit The slit in the roof of the mouth which connects to the bird's sinuses.

Cloaca The external opening to expel fecal matter. In birds there is a single opening for intestinal (fecal matter), urinal (urine and urates), and genital tracts.

Commissure The delicate corner of the mouth, also called the commissural point.

Coverts Row of feathers which run down the wing above the primaries and secondaries. This is the generally referred to feathers when somebody says "coverts". There are other covert feathers over the body such as those on the tail and over the alulas.

Crines The short hair-like feathers around the cere and beak.

Crop The crop of the bird is like a pouch along the esophagus. It is where food is initially placed before it moves into the stomach. Food comes here for quick storage and to soften it and to separate out the digestibles from the indigestibles. It is useful to note that owls have no crop.
This photo shows a bird just after eating. My index finger is at the bottom of her gorged crop and my second finger is resting above her crop. You can feel the enlarged pouch when a bird has a full crop and you can even separate the top layer of feathers to see the skin stretched over the crop.

Crural The feathers that cover the leg from the upper leg to the abdomen. In some species the crural feathers cover the leg to the top of the foot.

Deck The two center tail feathers in the train.

Ear Raptors have ears placed on each side of their head, although there is virtually no external structure to it.

Fret marks A line across feathers created when a bird is starved or diseased while she was growing the feather. Also called stress marks, stress bars, or hunger traces.

Gape Referring to the breadth of the bird's mouth opening from corner to corner. Sometimes people use this term to mean the opening of the mouth in general, but it specifically is referring to the opening across the delicate corners of the mouth, the gap. Often used with comments about how a particular hood is fitting.

Glottis The valve at the base of the tongue that closes the trachea to food or liquid.

Hallux The toe which faces backwards on most raptors. In hawks, this is the talon most responsible for puncturing the vitals of prey. Technically, this is labeled toe #1. The innermost forward toe is toe #2, the next toe outside of that is toe #3 and the furthest front-facing toe is toe #4. With regards to the feet, most raptors have three toes facing forwards and one toe facing backwards. This conformation is called Anisodactyl. Some birds, such as owls, have two toes facing forwards and two facing backwards. This conformation is called Zygodactyl. And then the Osprey has the unique ability to swivel her third toe to be in either conformation.

Keel The large bone running vertically up the bird's breast. This is the site of the breast muscle's attachment and is a very important bone. The term feel the keel means to put the keel between your thumb and finger and judge the amount of fat and muscle along the sides of this ridge. A healthy, well muscled bird will have a dense padding along the sides and barely any ridge of the bone to be felt. A bird who is in low condition will have a sharp ridge of bone sticking out with very little muscle or fat along side. A fat bird without a lot of muscle will be well padded, but not with dense muscle.
Because of the way that falcons are structured, they will tend to be better muscled than a comparable hawk. They depend on those muscles more than a hawk does and the muscles reflect that.

Mail The breast feathers.

Malar stripe The dark streak of feathers beneath a falcon's eye. The biological theory for this is that, much like athletes putting blacking under their eyes to prevent glare, this also prevents glare from reflecting off their feathers. The picture here shows a Lanner with the dark streak. Also called the facial stripe or eye stripe.

Mandible The upper and lower jaw and the beak. (Image also shows tongue and open beak.)

Nare The nasal opening in the cere. In falcons this is a circular opening, and in all member of Accipitradae this is an oval.

Nictitating membrane The nictitating membrane is sometimes called the third eyelid or the "haw". It is a thin, white membrane that can operate independently of the eyelid. The purpose is to have a form of protection over the eye while still retaining some amount of vision.
Note: In the graphic, the first image has the eye exposed and the membrane open while the second image shows the eye covered by the membrane. The arrow is pointing to the membrane

Pannel The stomach region (UK).

Patagial The "arm pit" region.

Pendant feathers The feathers behind the thighs (UK).

Preen gland Formally called the uropygial gland, this is a gland at the base of the tail that produces oil important to proper feather and beak health as well as waterproofing. The bird spreads this oil over the feathers and body through preening actions.
       Preen video clip: 562 Kb

Primaries The primaries provide the main forward thrust for flight. On the wing, these are the feathers most distal (located nearest to the tip; furthest from the center of the body). Also called beam feathers in the UK, flight feathers or phalangeal feathers.

Principals The longest two feathers on a hawk's wing.

Pygostyle The tail bone that supports the tail muscles and feathers.

Rectrices The paired tail feathers. There are, generally, 12 tail feathers in total. This is a term used in general biology, and not usually in falconry.

Remiges The primary and the secondary feathers are together called remiges.

Sarcel British term for the outermost primary feather.

Secondaries The feathers most proximal (just inside from the primary feathers; closer to the center of the body) on the wing are the largest surface area of the wing. Also called flags in the UK.

Superciliary Line The line of feathers above the eye similar to the eye brow.

Supraorbital ridge The ridge just above the eye; the brow bone. Immature birds are frequently not seen with a developed supraorbital ridge.

Talon A raptor's toe nail.

Tarsus The leg between the foot and first joint.

Tomial tooth The tooth (and often referencing the corresponding notch) in a falcon's beak specialized for snapping the neck of their prey. Sometimes just called the notch.

Trachea The tube at the back of the bird's tongue which leads to the lungs.

Train The 12 tail feathers. Formally called the retrices (singular retrix).

Vent The external surface of the cloaca. Birds are unique in that their fecal and urates come from a single outlet which is the cloaca. The fecal is the dark portion and is the stool. The urate is the white solid portion. The liquid clear-ish is the liquid urine.

Wing butts The forward angled section of the wing - analogous to our wrist.

More information on avian biology in general:
Plumage and moults - All About Birds: The Basics
Moult and plumage
Moult in Birds of Prey: A Review of Current Knowledge and Future Challenges for Research
Avian skeleton and biology

All images and text Copyright © 2004 - 2020 - Lydia Ash